Development of Roadway Weather Severity Index

Abstract

Winter weather conditions play a significant role in the operation of the surface transportation system, including heightening safety risks for motorists. Previous research has sought to correlate winter weather severity with maintenance costs through the use of indices, although few have been developed to relate winter weather parameters to safety. This paper summarizes a research project using data from California, Montana, and Oregon to quantify relationships between winter weather and safety. Many model forms were reviewed, and then linear models were developed to predict the cubic root of the crash rate as a function of weather parameters. Models were developed for different topographic zones and on a statewide level, with correlations ranging from 0.12 to 0.67. These models were used to develop indices that may be used for traveler information purposes. The indices show promise for application in traveler information and winter maintenance; therefore, recommendations for research are included.